1. Field of the Invention
The present invention relates to an image processing apparatus capable of handling an image in which information is embedded, to a method for controlling an image processing apparatus, and to a computer-readable medium.
2. Description of the Related Art
There is a known technique for printing a copy-forgery-inhibited pattern image, as described in, for example, Japanese Patent Laid-Open No. 2001-197297.
A copy-forgery-inhibited pattern image is an image in which a pattern of, for example, a character string is made visible when a printed material with the image printed thereon is copied. The copy-forgery-inhibited pattern image is composed of a set of large dots (latent image) and a set of small dots (background image). Because the small dots are too small to be accurately reproduced by a copier, only an area where the large dots (latent image) are present is reproduced on a duplicate. As a result, a pattern, for example, a character string, is made visible. In this case, the set of large dots forms the pattern of, for example, a character string. The copy-forgery-inhibited pattern image is useful for preventing leakage of secret information through a printed material by representation of tracking information as the pattern of, for example, a character string. To prevent leakage of secret information in such a way, the tracking information typically contains information about a user who requested printing (e.g., user name) and a printing time.
A technique for printing an encoded image is also well known. The encoded image used here indicates a two-dimensional or linear bar code image and a digital watermark image formed by a digital watermarking technique. The technique for printing an encoded image is effective at preventing leakage of confidential documents by including important information, such as tracking information, into the encoded image.
In addition, a technique for printing each component of a two-dimensional code image as large dots in a copy-forgery-inhibited pattern image is also well known, as described in, for example, Japanese Patent Laid-Open No. 2002-305646. In this patent document, dots representing the shape of / or \ are printed as large dots. By the definition of that the mark / indicates 0 and the mark \ indicates 1, information (e.g., tracking information) is printed as the large dots of a copy-forgery-inhibited pattern image.
As described above, techniques for embedding information, such as the technique for printing a copy-forgery-inhibited pattern image, the technique for printing an encoded image, or the technique for printing an encoded image in a large-dot area of a copy-forgery-inhibited pattern image, are being actively developed in recent years. The techniques are of great utility in preventing leakage of secret information by, for example, embedding tracking information.
Copiers typically have the function of removing a specified color, as described in, for example, Japanese Patent Laid-Open No. 2004-228896. This function is that a user specifies a color that the user wants to remove in copying a document and a document image obtained by scanning of the document is printed such that the specified color is removed from the document image. One example characteristic is that removing red from a document in which a user added the red with a red pen allows a duplicate of the document prior to the addition.
However, when the technique disclosed in this patent document is applied to an image in which information is embedded, an area where the information is embedded will be deleted. As a result, for example, tracking information will be invisible, and this will encourage leakage of secret information.